The present invention relates to a liquid crystal display apparatus equipped with a transparent touch panel capable of preventing a decrease in the visibility, which is caused by the reflection of external light, when it is mounted on liquid crystal cell, and to a touch panel used in the apparatus.
Recently, an attention is focused on the liquid crystal display element as an image display element, and it is expected the liquid crystal display apparatus is applied to a portable electronic databook, data terminal, the view finder of a video camera, the monitor of a car navigator, as a kind of its usage. These days, there is a demand of an input method, in which a transparent touch panel is placed on the display element of each of these devices as an input device, and an input can be made while monitoring the screen. Conventionally, in such usage, a so-called resistance-film type touch panel, which is a touch panel manufactured with use of polyethylene terephthalate (PET) film having a transparent conductive film thereon and glass having a transparent conductive film thereon, is stacked on a liquid crystal display element to be used.
Meanwhile, as the usage of the touch panel widens, there are demands created, such as the improvement of the contrast of the display and the prevention of the reflection of external light, and therefore a technique of integrating a touch panel and a liquid crystal display apparatus together is attempted. Such a technique is, as described in Jpn. Pat. Appln. KOKAI Publication No. 10-48625, a liquid crystal display apparatus, in which a touch panel is provided between a display surface-side polarizing plate and cell having a liquid crystal material sealed between transparent electrode substrates (to be called as liquid crystal cell hereinafter), and further a retardation corresponding to a xc2xc wavelength to visible light is imparted to the transparent conductive substrate constituting a touch panel, or corresponding xc2xc wave plates are adhered together, so as to build a touch panel therein, thus preventing internal reflection light. In particular, from the display surface side, a polarizing plate, a xc2xc wave plate A, a touch panel, a xc2xc wave plate B and a liquid crystal cell are arranged in the order, and further slow axes of the xc2xc wave plates A and B are arranged to be in parallel or perpendicular with each other, so as to prevent the return of light to the display surface due to the reflection of external light by the xc2xc wave plate A. Further, undesirable coloring on the display and a decrease in contrast, which are caused by the xc2xc wave plate A, can be prevented by the xc2xc wave plate B.
In the case of the above-described structure, it is necessary that the polarization light axis of polarized light emitted from the liquid crystal cell in the cases where a voltage is applied to liquid crystal and where it is not, the polarization axis of the display surface-side polarizing plate, and slow axes of the xc2xc wave plates A and B within a film surface, satisfy such a relationship that a diagonal position, that is, the difference in axial angle between the polarization axis and the slow axis of the xc2xc wave plate, becomes 45xc2x0. In the case of liquid crystal display apparatus of an ordinary twist nematic type, a typical example of which is a thin-film transistor liquid crystal display device (TFT), the polarization axis of emitted light from a liquid crystal cell while a voltage is applied or not applied to the cell makes 45xc2x0 or 135xc2x0 in many cases, and similarly, the polarization axis of the polarizing plate on the display surface side makes 45xc2x0 or 135xc2x0. (Note that the absolute angle of each axis is set to 0xc2x0 in the horizontal direction as viewed from the display surface side, and it increase positively in the counter-clock wise direction, as shown in FIG. 1.) Therefore, the slow axis of the xc2xc wave plate is arranged towards the 0xc2x0 or 90xc2x0 direction.
In the meantime, the xc2xc wave plate industrially produced, a typical example of which is a retardation film, is prepared by cutting a continuous roll-shaped retardation film of 100 m or more, into necessary sizes, and the slow axis is directed in the long side direction of the roll-shaped film (the machine length direction, to be called MD direction, hereinafter), or in the width direction of film (to be called TD direction). Therefore, the roll-shaped retardation film can be cut into display sizes at high yield by matching the display surface side direction with the MD or TD direction.
In the case of a liquid crystal display apparatus which does not have the above-described structure, that is, for example, in the case of a liquid crystal display apparatus such as of a special TN type, or an STN type having a super-twist nematic structure, the polarization axis of the emission light from the liquid crystal cell does not make 45xc2x0 or 135xc2x0 as in the former TN type, or in many cases, the polarization axis differs depending on the transmission wavelength. Therefore, it is necessary to arrange the slow axes of xc2xc wave plates A and B to be inclined in accordance with the emission light polarization axis, in order to reduce the reflection light and minimize the change in color tone. Thus, it is necessary to cut the xc2xc wave plate at an angle with respect to the TD direction of the roll-shaped retardation film, which causes a remarkable reduction of the yield.
Usually, as the surface side substrate of the touch panel, a thin glass plate or plastic film optically isotropic, which has a transparent conductive layer, is used. However, in the case of the plastic film, it generally has a low retardation of about 5 to 20 nm, and its slow axis is directed to the MD or TD direction. Therefore, as can be seen in Jpn. Pat. Appln. KOKAI Publication No. 10-186136, there has been a proposal that its slow axis is arranged to be parallel with the slow axis of the xc2xc wave plate A so as to adjust the sum of the retardation values of both. Here, in the case where the slow axis of the xc2xc wave plate is arranged to be inclined as described above, the plastic film having a transparent conductive layer should necessarily be cut and arranged inclined to be along the xc2xc wave plate. Therefore, not only the xc2xc retardation film, but also the film having the transparent conductive layer will have a remarkable decrease in the yield.
Further, there is an attempt that a xc2xc wave plate is cut out from the roll-shape retardation film on which a touch panel transparent electrode is formed, and the xc2xc wave plate and the electrode substrate are integrated with each other with such a structure, the layer structure on the touch panel display surface side (input surface side) becomes simple, and therefore the tool force necessary for input becomes simple. It is, further, advantageous that the production cost is lowered. However, as already described, the attempt entails a problem that the yield significantly decreases due to the fact that the layer need be cut to be inclined with respect to the film TD direction. Further, the film includes the roll-shaped retardation film which has been subjected to the secondary process including the transparent conductive process, which is an expensive film, and therefore the production cost will be markedly increased.
In order to solve the above-described problem, the inventors of the present invention made intensive studies, and found that with newly use of a xc2xd wave plate having a retardation of xc2xd wavelength with respect to visible light, the slow axes within the film surfaces of xc2xc wave plates A and B can be arranged substantially in a direction of 0xc2x0 or 90xc2x0 without deteriorating the optical characteristics, which has matured into the present invention.
Further, they found that the slow axis within the film surface of the xc2xc wave plate A can be arranged substantially in a direction of 0xc2x0 or 90xc2x0 without deteriorating the optical characteristics, and thus the yield can be improved, by the relative angle between the two xc2xc wave plate delay axes is shifted from vertical crossing or running in parallel with each other while the relative arrangements with respect to the polarization axis angle of emitted light from the polarizing plate and liquid crystal cell.
Thus, according to the first aspect of the present invention, there is provided a touch-panel equipped liquid crystal display apparatus comprising: a polarizing plate A; a xc2xc wave plate A; a touch panel; a xc2xc wave plate B; and a liquid crystal cell, which are disposed in the above-mentioned order from the display surface side, characterized in that at least one xc2xd wave plate C is arranged at a position between the display surface side polarizing plate A and the liquid crystal cell, and the slow axis within the film surface of the xc2xc wave plate A is set substantially in a direction of 0xc2x0 or 90xc2x0.
Further, according to the second aspect of the present invention, there is provided a touch-panel equipped liquid crystal display apparatus according to the first aspect, wherein the xc2xc wave plates A and B, the xc2xd wave plate C and the touch panel are laminated into an integral body, and the xc2xc wave plate A is laminated on the display surface side of the touch panel, whereas the xc2xc wave plate B and the xc2xd wave plate C are laminated on the opposite side surface of the touch panel.
According to the third aspect of the present invention, there is provided a touch-panel equipped liquid crystal display apparatus comprising: a polarizing plate A; a xc2xc wave plate A; a touch panel; a xc2xc wave plate B; and a liquid crystal cell, which are disposed in the above-mentioned order from the display surface side, characterized in that the slow axis within the film surface of the xc2xc wave plate A is set substantially in a direction of 0xc2x0 or 90xc2x0, the slow axis within the film surface of the xc2xc wave plate B is set substantially at a diagonal position to the direction of the polarization axis direction of the emitted light from the liquid crystal cell, and the slow axes of the xc2xc wave plates A and B are arranged not in parallel with each other, or not cross over at right angles.
Further, according to the fourth aspect of the present invention, there is provided a touch-panel equipped liquid crystal display apparatus according to the third aspect, wherein the xc2xc wave plates A and B, and the touch panel are laminated into an integral body, and the xc2xc wave plate A is laminated on the display surface side of the touch panel, whereas the xc2xc wave plate B is laminated on the opposite side surface of the touch panel.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.